The present invention relates to crankcase lubricating oil compositions. More particularly, the present invention relates to such compositions which have relatively low levels of phosphorus and sulfur and exhibit acceptable compatibility with the Viton(copyright) fluoroelastomer seals used in internal combustion engines.
Zinc dihydrocarbyl dithiophosphates (ZDDP""s) have been the principal antiwear additives in the lubricating oil field and are normally used such that the finished oil will have a phosphorus-content of about 0.1% by weight or higher in order to meet industry performance tests for wear reduction. Another advantage of ZDDP""s has been their ability to contribute to the compatibility of the lubricant with fluorocarbon elastomers, such as those referred to as Viton(copyright) elastomers. To comply with regulations and manufacturers"" specifications, the trend in the lubricating oil industry is to reduce the amount of both phosphorus and sulfur in crankcase lubricants in order to improve the durability of exhaust gas after-treatment systems. ZDDP""s, which contains both these elements, are a major contributor of both phosphorus and sulfur in lubricating oil compositions.
A problem in formulating lubricating oil compositions that contain low levels of ZDDP and corresponding low levels of phosphorus and sulfur is the consequent adverse performance in the Volkswagen Viton(copyright) seal compatibility test, specifically the Volkswagen PV 3344 Seal Test, which is currently considered the most difficult fluoroelastomer seal compatibility test applicable to commercial lubricating oils. The present invention ameliorates the problem, as evidenced by the data provided herein, by using a nitrogen-containing lubricating oil dispersant in combination with a nitrogen-free lubricating oil dispersant, as well as a hydrocarbyl-substituted carboxylic acid or derivative thereof such as an anhydride.
EP-A-0 277 729 describes lubricating oils having a phosphorus content not greater than 0.1 wt 1%. Such oils are not described as containing nitrogen-free dispersants or hydrocarbyl-substituted carboxylic acids or derivatives thereof, nor are their fluoroelastmer seal compatibility properties addressed.
The present invention provides, in a first aspect, a crankcase lubricating oil composition comprising:
(A) an oil of lubricating viscosity, in a major amount;
(B) a nitrogen-containing lubricating oil dispersant, in a minor amount, such as 1.5 to 2 mass %;
(C) a nitrogen-free lubricating oil dispersant, in a minor amount, such as 1 to 1.5 mass %;
(D) a metal dihydrocarbyl dithiophosphate, in a minor amount, such as 0.25 to 0.8 mass %;
(E) a hydrocarbyl-substituted carboxylic acid or derivative thereof, such as an anhydride, in a minor amount such as 0.25 to 0.8 mass %; and
(F) a metal detergent, in a minor amount such as 0.1 to 4 mass %,
wherein the mass:mass ratio of (B) to (C) in the composition is 0:4:1 or greater, such as in the range from 10:1 to 0.4:1, and the composition contains 0.075 or less, preferably 0.06 or less, more preferably 0.05 or less, mass % of phosphorus, expressed as elemental phosphorus. The composition may be phosphorus-free or contain from 0.01, or from 0.02, mass % phosphorus.
In a second aspect, the invention provides the use of components (B) to (F), as defined in the first aspect of the invention, in a lubricating oil composition that contains 0.075 or less, preferably 0.06 or less, more preferably 0.05 or less, mass % phosphorus, expressed as elemental phosphorus, to improve the fluoroelastomer seal compatibility properties of the composition.
In a third aspect, the invention provides a method of lubricating an internal combustion engine equipped with an exhaust gas after treatment system which comprises supplying to the engine a lubricating oil composition according to the first aspect of the invention.
In this specification:
xe2x80x9cMajor amountxe2x80x9d means in excess of 50 mass % of the composition.
xe2x80x9cMinor amountxe2x80x9d means less than 50 mass % of the composition, both in respect of the stated additive and in respect of the total mass % of all of the additives present in the composition, reckoned as active ingredient of the additive or additives.
xe2x80x9cComprises or comprisingxe2x80x9d or cognate words are taken to specify the presence of stated features, steps, integers, or components, but does not preclude the presence or addition of one or more other features, steps, integers, components or groups thereof.
xe2x80x9cTBNxe2x80x9d is Total Base Number as measured by ASTM D2896.
xe2x80x9cOil-solublexe2x80x9d or xe2x80x9coil-dispersiblexe2x80x9d do not necessarily indicate that the additives are soluble, dissolvable, miscible or capable of being suspended in the oil (A), in all proportions. They do mean, however, that they are, for example, soluble or stably dispersible in the oil to an extent sufficient to exert their intended effect in the environment in which the oil is employed. Moreover, the additional incorporation of other additives may also permit incorporation of higher levels of a particular additive, if desired.
All percentages reported are mass % on an active ingredient basis, i.e., without regard to carrier or diluent oil, unless otherwise stated.
It should be noted that the lubricating oil compositions of this invention comprise defined individual, i.e. separate, components that may or may not remain the same chemically before and after blending. Thus, it will be understood that the various components of the composition, essential as well as optimal and customary, may react under the conditions of formulation, storage or use, and that the invention also provides the product obtainable or obtained as a result of any such reaction.